• Composites Research
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• v.23 no.1
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• pp.8-16
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• 2010

The Fiber/Metal Laminates (FMLs) have been developed as a new composite material for aerospace application to reduce weight and improve damage tolerance. In this study, firstly FMLs were manufactured and the tensile test was performed to investigate the mechanical properties of FMLs. Furthermore, impact behavior of the low velocity on FMLs which consisted of different types of aluminum or fiber/epoxy layers was tested by the drop weight impact tester based on the different impact energy conditions. The load-time and energy-time curves were employed to evaluate the impact performance of different specimens. Moreover, finite element analysis (FEA) was also performed to simulate the tensile test and impact behavior of FMLs under the same conditions with the tests and good agreements have been obtained between the FEA predictions and experimental results.

• Composites Research
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• v.23 no.3
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• pp.13-18
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• 2010

One of the biggest challenges in the nano-field is how to effectively disperse nano-scale particles, especially CNTs, which are strongly agglomerated by intermolecular van der Waals forces. This study suggests a new method, discharge flocking, in order to disperse nano-scale particles effectively, which combines corona discharge phenomenon and a traditional electrostatic flocking process. In order to evaluate the discharge flocking process, composite specimens were fabricated by the process and RFI(resin film infusion) process, and then the mechanical and electrical properties of the specimens were measured and compared. Moreover, the evaluation of gas discharge effect on the CNTs and epoxy was performed to compare the mechanical and electrical properties of the composite specimens including the plasma treated CNTs. The experimental results showed that the electrical and mechanical properties of the specimens fabricated by the discharge flocking process were similar to those of the RFI process. In addition, plasma treated CNTs were not affected by gas discharge during the discharge flocking process.

• Composites Research
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• v.26 no.1
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• pp.21-28
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• 2013

The ballistic limit of Carbon/Epoxy composite laminates with the finite effective area are predicted by using the quasi-static perforation test and semi-empirical formula. The perforation energy were calculated from force-displacement curve in quasi-static perforation test. Also, the actual ballistic limit and penetration energy were obtained through the high-velocity impact test. The quasi-static perforation test and high-velocity impact test were conducted for the specimens with 3 different effective areas. In the high-velocity impact test, the air gun impact tester were used, and the ballistic and residual velocity was measured. The required inputs for the semi-empirical formula were determined by the quasi-static perforation tests and high-velocity impact tests. The comparison between semi-empirical formula and high-velocity impact test results were conducted and examined. The ballistic limits predicted by semi-empirical formula were agreed well with high-velocity impact test results.

• Composites Research
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• v.30 no.1
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• pp.15-20
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• 2017

In this study, LIPCA-S2 actuator with a piezoelectric single crystal layer and a carbon/epoxy layer was designed and evaluated to increase actuation performance of piezo-composite unimorph actuator. A curvature change model generated by the induced strain of a piezoelectric layer was used to predict the tip displacement of the piezo-composite unimorph cantilever. However, we found that there was big difference between the predicted and the measured tip displacement of LIPCA-S2 cantilever actuator when we used the previous linear prediction model. A new prediction model considering the change of piezoelectric strain coefficient and elastic modulus for the compression stress variation of the PMN-29PT single crystal layer was used and it was found that the difference between the predicted and the measured tip displacement reduced considerably.

• Composites Research
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• v.12 no.5
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• pp.40-53
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• 1999

The interlaminar facture behavior of multidirectional carbon-fiber/epoxy composite laminates under low and high rates of test, up to rate of about 11.4m/s has been investigated using the double cantilever beam specimens. The mode I loasing with rates above 1.0m/s had considerable dynamic effects on the load-time curves and thus revealed higher values of the average crack velocity than thet expected from a simple proportional relationship with the test rate. The modified beam analysis utilizing only the opening displacement and crack length exhibited an effective means for evaluating the dynamic fracture energy $G_{IC}$. Flexural modulus increased gradually with an increase of the test rate, which was utilized in the evaluation of $G_{IC}$. Values of $G_{IC}$ at the crack initiation and arrest were scarcely changed with increasing test rate up to 1.0m/s. However the maximum $G_{IC}$ was much enlarged at 11.4m/s due to the large amount of fiber bridging the crack tip. The larger the initial crack length, the smaller the maximum $G_{IC}$ at high rate.

• Composites Research
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• v.33 no.1
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• pp.1-6
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• 2020

Dispersion and electrical resistance (ER) properties of polyurethane (PU) type topcoat were evaluated using carbon nanotube (CNT) with different CNT weight fraction. CNT was dispersed in PU type topcoat using ultra sonication dispersion method. CNT/PU topcoat was coated on carbon fiber reinforced epoxy composite (CFRC) surface using gravity feed spraying method. Static contact angles of CFRC and CNT/PU topcoat were performed using 4 types of solvents to calculate the work of adhesion between CNT/PU topcoat and CFRC surface. Surface resistance of CNT added PU topcoat was measured to determine CNT dispersion. Adhesion property between CNT/PU topcoat and CFRC was determined via cross hatch cutting test based on ASTM D3359. The optimized condition of CNT weight fraction was found.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.41 no.3
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• pp.187-192
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• 2017

This paper presents an ongoing study to develop a novel pressure sensor by means of a Nano Carbon Piezoresistive Composite (NCPC). The sensor was fabricated using the 3D printing process. We designed a miniaturized cantilever-type sensor electrode to improve the pressure sensing performance and utilized a 3D printer to build a small-sized body. The sensor electrode was made of 2 wt％ MWCNT/epoxy piezoresistive nano-composite, and the sensor body was encapsulated with a pipe plug cap for easy installation to any pressure system. The piezoresistivity responses of the sensor were converted into stable voltage outputs by using a signal processing system, which is similar to a conventional foil strain gauge. We evaluated the pressure-sensing performances using a pressure calibrator in the lab environment. The 3D-printed cantilever electrode pressure sensor showed linear voltage outputs of up to 16,500 KPa, which is a 200％ improvement in the pressure sensing range when compared with the bulk-type electrode used in our previous work.

• Bulletin of the Society of Naval Architects of Korea
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• v.25 no.4
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• pp.58-68
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• 1988

This paper is concerned with mechanical properties of unidirectional laminate $[(0^{\circ})_{8T},\;(90^{\circ})_{8T}]$, composed of angle plies $[({\pm}15^{\circ})_{2S},\;({\pm}30^{\circ})_{2S},\;({\pm}45^{\circ})_{2S},\;({\pm}60^{\circ})_{2S},\;({\pm}75^{\circ})_{2S}$ and laminate $[(9^{\circ}/90^{\circ})_{2S},\;(90^{\circ}/{\pm}45^{\circ}/0^{\circ})_S,\;({\pm}45^{\circ}/0^{\circ}/{\pm}90^{\circ})_S,\;({\pm}45^{\circ}/90^{\circ}/0^{\circ})_S,\;(0^{\circ}/90^{\circ}/{\pm}45^{\circ})_S,\;(90^{\circ}/0^{\circ}/{\pm}45^{\circ})_S]$ under the condition of uniform strain tension. Also, experimental investigation was conducted $[10]_{8T}$, off-axis tensile test for intralaminar shear characterization. The experimental data on the failure criterion of tensor polynomial were compared with those from the classical laminate theory. Acoustic Emission experiments have been carried out to investigate the changes of the amplitude distributions of Acoustic Emission monitored during failure of tensile tests on Carbon/Epoxy composites.

• Corrosion Science and Technology
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• v.14 no.5
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• pp.213-217
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• 2015

Recently, household electronic industries require environmentally-friendly and highly functional steels in order to enhance the quality of human life. Customers especially require both excellent corrosion and abrasion resistant anti-fingerprint steels for digital TV panels. Thus POSCO has developed new functional electro-galvanized steels, which have double coated layers with organic-inorganic composites on the zinc surface of the steel for usage as the bottom chassis panel of TVs. The inorganic solution for the bottom layer consists of inorganic phosphate, magnesium, and zirconium compounds with a small amount of epoxy binder, and affords both improved adhesion properties by chemical conversion reactions and corrosion resistance due to a self-healing effect. The composite solution for the top layer was prepared by fine dispersion of organic-inorganic ingredients that consist of a urethane modified polyacrylate polymer, hardener, silica sol and a titanium complex inhibitor in aqueous media. Both composite solutions were coated on the steel surface by using a roll coater and then cured through an induction furnace in the electro-galvanizing line. New anti-fingerprint steel was evaluated for quality performance through such procedures as the salt spray test for corrosion resistance, tribological test for abrasion resistance, and conductivity test for surface electric conductance regarding to both types of polymer resin and coating weight of composite solution. New composite coated anti-fingerprint steels afford both better corrosion resistance and abrasion properties compared to conventional anti-fingerprint steel that mainly consists of acrylate polymers. Detailed discussions of both composite solutions and experimental results suggest that urethane modifications of acrylate polymers of composite solutions play a key role in enhanced quality performances.

• Elastomers and Composites
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• v.51 no.4
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• pp.342-349
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• 2016

Characteristics of the swelling-induced wrinkles on the surfaces of natural rubber (NR) film were investigated. The wrinkle structure was generated by swelling of NR film pre-stretched and firmly bonded onto an aluminum substrate in hexane. A novel experimental method was adopted to replicate the swelling-induced wrinkles on the NR film using an epoxy-hardener system. To get insight into the wrinkle parameters; the wrinkle length (L), wrinkle distance (D), wrinkle height (H) and the angle between two consecutive wrinkles (${\theta}$), the cross-sections of the replicas obtained from saturated swollen NR film were examined using an optical microscopy (OM). From the OM images, the wrinkling parameters were measured as a function of the thickness of NR film from 0.42 to 1.76 mm. Also, it was evaluated that the effects of swelling time on the wrinkling parameters. The length (L), distance (D) and height (H) of wrinkles increased as the thickness of the NR film and the swelling time increased. However, the angle between the wrinkles (${\theta}$) showed a sharp decrease up to a swelling time of 200 minutes and slightly decreased afterwards.